Clay Minerals in Pore Spaces, Improving or Reducing Reservoir Quality - A Siliciclastics Reservoir of Northeast Iran

Abstract

Sandstones, due to their interagranular pore space are important reservoir rocks in petroleum industry. Clay minerals are often one of the common substances in sandstone rocks, and in their presence they affect porosity and permeability effectively. Identification of the types of clay minerals in sandstones is therefore a key to understanding their reservoir quality. This study is focused on the origin, formation, diagenetic processes and eventually influence of clay minerals on reservoir quality in one of the clastic reservoirs in northeast of Iran by XRD, XRF and SEM analysis, together with more than 2000 petrographical thin sections examination. The results indicated that altered feldspars and albeit with low amount of hematite are the main sources for clay minerals. Clay minerals can destroy permeability in sandstones rocks but chlorites grain-coating in this quartz-rich sandstones can help to preserve porosity and permeability, they also impede quartz overgrowths on quartz grains in this sandstone reservoir. Time and temperature of chloride coating formation were deduced from chloride rim thickness around the quartz grains. On the other hand occurrence of illite in this reservoirs is mainly related to the reaction of K from feldspar with kaolinite, which has reduced the reservoir quality.